21 In approaching therefore, come not with your wrists extended, or your fingers spread; but make your left hand a throne for the right, as for that which is to receive a King. And having hollowed your palm, receive the Body of Christ, saying over it, Amen. So then after having carefully hallowed your eyes by the touch of the Holy Body, partake of it; giving heed lest you lose any portion thereof; for whatever you lose, is evidently a loss to you as it were from one of your own members. For tell me, if any one gave you grains of gold, would you not hold them with all carefulness, being on your guard against losing any of them, and suffering loss? Will you not then much more carefully keep watch, that not a crumb fall from you of what is more precious than gold and precious stones?
Source: Catechetical Lectures (New Advent)